Background Art
Space propulsion systems using solar thermal energy have been proposed as a means to achieve greater payload fractions. These engines can be used, for example, to provide thrust to boost payloads from low earth orbits to higher orbits or to alter the orbit of a payload. In such engines, solar radiation is captured and focused by mirrors into a "black body" where the solar radiation is used to heat a propellant, such as hydrogen. The propellant is then passed through a nozzle to create thrust.
To further reduce the weight of the orbit transfer vehicle and increase the payload fraction, U.S. Pat. No. 5,459,996 entitled "Hybrid Solar Rocket Utilizing Thermal Storage for Propulsion and Electrical Power", the disclosure of which is hereby incorporated by reference as if fully set forth herein, has suggested a solar thermal rocket engine that utilizes energy conversion diodes to convert stored thermal energy into electrical energy. This configuration, however, does not reduce the weight of the orbit transfer vehicle to the maximum extent possible due to the relative inefficiency with which stored thermal energy is converted into electrical energy. The inefficiency of this process necessitates the use of a large and relatively heavy thermal storage device.